The early or transforming region of Simian Virus 40 encodes the T Ags (tumor antigens) and induces TSTA (the tumor specific transplantation antigen). The primary objectives of this research are threefold: 1) to study by physical methods and affinity columns key reactions of large T Ag (self-association, nucleotide and DNA binding, and interaction with the new 48K-55K phosphoprotein species) which are important to understanding its probable enzymatic activity in initiating DNA synthesis; (2) to characterize the new 48K-55K phosphoprotein species (isolated in my laboratory) by a) mRNA isolation and in vitro translation and b) preparation of specific antisera to determine whether they are either 1) virus coded or 2) host coded, but virus-induced or modified; and 3) to characterize the new putative cell-surface (PCS) glycoprotein species recently isolated in my laboratory, which cross-reacts with large T Ag by comparison of its tryptic fingerprint with large T Ag. In addition we will determine by immunization with the isolated PCS whether it is related to TSTA, the viral antigen mediating tumor rejection. Unique to this work has been our use of antisera to pure large T Ag to isolate new species which may be the postulated viral products such as TSTA.